Many types of electronic devices are used for communication and entertainment purposes. Electronic devices include devices such as cellular phones, smartphones, mobile communication devices, tablets, computers, cameras, video players, electronic media readers, audio players, handheld scanners, two-way radios, global positioning satellite (GPS) devices, and other types of electronic computing or communication devices, including combinations thereof. These devices often contain sensitive or fragile components, such as electronic components or glass screens, which can be easily damaged if the device is dropped or exposed to substantial forces. To protect the device from damage, it can be installed in a protective enclosure.
Electronic devices are commonly powered by one or more internal batteries. These batteries are often rechargeable. Typically, devices with more computational power and/or larger displays consume the available battery power more quickly. If an electronic device's battery is exhausted, the device may become unusable until the battery can be recharged or until the device can be connected to another power source. Battery capacity often becomes an issue due to factors such as: power requirements of the electronic device, extended usage of the electronic device, physical space constraints of the battery, power requirements of peripherals attached to the electronic device, temperature extremes, unavailability of a power source for charging, decreased battery capacity due to aging of the battery, decreased battery life due to the number of charge/discharge cycles a battery has endured, or combinations thereof. These factors can reduce the usefulness of electronic devices because use time of the device between recharges becomes shorter and the user must typically recharge the device before use can continue.
In some situations, a user may carry a spare battery for the electronic device that has been previously charged but is not electrically connected to the electronic device. The spare battery can be used as a replacement for a discharged battery. While carrying the spare battery enables the user to use the device again without having to find a charging source, this approach has drawbacks. First, the user must remember to carry the spare battery(s), in addition to the electronic device, because the spare battery will not typically be physically attached to the electronic device when not in use. Second, replacing an exhausted battery, or swapping an exhausted battery into the electronic device for charging purposes, typically requires that the device be shut down, or otherwise turned off, and restarted or rebooted. This process is often inconvenient and typically results in temporary loss of communication and/or data. Finally, when a charging source is available, the various batteries must be swapped into and out of the electronic device in order to charge them, unless a separate host charging device is available for the extra battery.
In some situations, some of the problems discussed above are resolved through use of a supplemental battery pack that attaches to the electronic device. The battery pack is mechanically and electrically attached to the electronic device in a manner such that the electronic device can make use of both its internal battery and a supplemental battery in the battery pack without having to shut down the electronic device, or otherwise temporarily remove power from the electronic device. However, existing solutions have drawbacks.
From an electrical standpoint, existing solutions take one of two approaches regarding how the two batteries (a battery in the external case for the electronic device and a battery inside the electronic device itself) are charged. In one approach, the two batteries are used and/or charged alternately. At any point in time the electronic device is only utilizing one of the batteries or is only charging one of the batteries. When the batteries are not being charged and one of the batteries becomes discharged, or becomes sufficiently low in power, the electronic device and/or the case switches usage from one of the batteries to the other. This approach has the limitation that one of the batteries may be exhausted before use of the other begins. If the internal battery is exhausted first and the electronic device is operating off of the supplemental battery, the user no longer has the flexibility of removing the supplemental battery/case from the device and using the electronic device without it.
In an alternate approach, both batteries are used and/or charged simultaneously as if they are a single battery. This approach presents several problems. First, the user and/or the electronic device cannot selectively control which of the batteries is charged first. Second, charging batteries in parallel may not be a preferred method if the batteries have different characteristics. Third, charging both batteries simultaneously may draw too much current from the power source and/or otherwise exceed the specifications of the power source. For example, a Universal Serial Bus (USB) interface may only be specified to provide 500 mA (milliamperes) of current and charging both batteries simultaneously may exceed that limit. Drawing too much current from a power source may damage the power source, may damage the device that hosts the power source (i.e., the computer in which a USB port is located), may cause the power source to overheat, or may cause the power source or host device to enter a failsafe mode which discontinues power until the power source or host device is reset and/or rebooted.